Thermionic amplifier for use in conjunction with photo-electric devices



Oct. 25, 1932.

THERMIONIC AMPLIFIER w. F. TEDHAM 1,884,376

FOR USE IN CONJUNCTION WITH PHOTO EIJEGTRTC DEVICES Filed June 24, 1.950

A [nven tor mg g Patented Oct. 25, 11932 UNITED STATES PATENT orl-"lcr.

WILLIAM FRANCIS TEDHAM, OF LONDON, ENGLAND, ASSIGNOR TO 'VICTOR TALKING MACHINE COMPANY, A. CORPORATION OF NEW JERSEY THERMIONIC AMPLIFIER FOR USE IN CONJUNCTION WITH PHOTO-ELECTRIC DEVICES Application filed June 24, 1930, Serial N 0. 463,419, and in Great Britain July 3, 1929.

The present invention relates to thermionic amplifiers for use in conjunction with photoelectric devices.

It is an object of the'present invention to improve the frequency response characteristic of apparatus of this kind more particularly at the higher acoustic frequencies.

According to the present invention in a thermionic amplifier having aphoto-electric device arranged in the input circuit thereof, a choke coil is arranged so as to be effectively in series with the oscillations derived from the photo-electric device. Thus the choke may be arranged in series between the photoelectric device and the grid circuit of a thermionic valve, or in addition to orin place of this choke, a choke may be disposed in series between the anode circuit of the first valve and the grid circuit of the second, or in a similar the amplifier.

It has been found that with this arrangement the overall frequency-response characteristic of the photo-electric device and the amplifier is improved.

The invention will be of example with reference ing drawing in which,

Fig. 1 is the circuit diagram of a thermionic amplifier embodying the invention;

Fig. 2 shows a modification of theinvention as applied to the circuit of Fig. 1, and

Fig. 3 is a diagram showing the type of response characteristics obtained with the circuit arrangements of Figs. 1 and 2.

In the following description suitable described by way to the accompanyvalues are given for various components'but.

these must not be taken as limiting the scope V of the invention.

Referring to Fig. 1 a photo-electric cell 1 is shunted by a resistance 2 of 0.5 megohms and one terminal of the photo-electric cell is connected to the filament of a thermionic valve 3. The other terminal of the cell is connected, on the one hand, through a resistance 4: of 0.5 megohms to the positive terminal of a high tension source, of, for example, 200

volts, and, on the other hand, through a condenser 5 of 0.2 microfarads and an inductance position in some later stage of connected through, a grid leak 6 of 0.5

megohms to a point atsuitable negative potential with respect to the filament. The anode of the valve 3 is connected to a positive terminal of the above mentioned high tension source through a choke coil 7, the negative terminal of this source being connected to the filament-of the valve. The anode of the valve is connected through a condenser 11 and an inductance such as a choke coil 10, to the input circuit of a second valve 8. Any desired number of stages of amplification may of course be added.

The inductance or choke 9 may be of 0.6

. henries and is connected in series between the photo-electric cell and the grid of the valve 3.

In addition to as shown or inplace of this choke, the choke 10 may be disposed in series between the anode circuit of the first valve and the in a similar position in some later stage of the amplifier. For this purpose the anode of the valve 3 may be connected to the grid of the valve 8 through the condenser 11 and the choke 10 after the manner of condenser 5 and choke 9, in series. constitutes with the tube resonant circuit. This arrangement causes the building up of the high frequency end of the response characteristic.

In some cases it has been found desirable to include in shunt across the grid circuit of the second valve a filter circuit comprising a condenser 12, Fig. 2, of 0.0005 microfarads in parallel with a choke 13 of 1.75 henries in series with a resistance 14 of 20,000 ohms.

In Fig. 3, curves A, B and C show the order of the overall response at different frequencies that has been obtained with the arrangements shown in Figs. 1, 2 and 3 respectively, the same photo-electric device being used in each case. It is evident from these curves that there is an improvement in the overall response at the with the arrangements shown in. Figs. 2 and 3.

I claim:

1. In an amplifying system for photogrid circuit of the second or The choke coil 9. capacity a series.

higher frequencies 7 electric currents, a light sensitive cell, a thermionic relay, means for coupling said cell to the input of said relay, and a choke coil in series between said cell and said input whereby the frequency response characteristic is accentuated for higher audio frequency.

2. In an amplifier for photo-electric currents as set forth in claim 1 characterized in that the output circuit of said relay comprises the combination of an audio frequency choke coil and resistor in series and a condenser in shunt with said series combination. i

In testimony whereof I have signed my name to this specification.

WILLIAM FRANCIS TEDHAM. 

